The field of the invention pertains to audio loudspeakers used in plural to realistically recreate the direct and ambient sound of an audio only, or an audio visual work such as a movie or television program and, in particular, in a home theater setting to provide sound from all directions to the viewer-listener. This invention also pertains to audio loudspeakers used for reproducing in a more realistic manner audio recordings in general (“auralization”).
Stereophonic sound systems utilizing two loudspeakers, both being forward of the listener, are common. More recently bass units (subwoofers) have been added as a third separate loudspeaker. The main purpose of adding this third speaker is to allow smaller left and right speakers, thus increasing the overall convenience of the sound installation. In home theater settings the two loudspeakers have been to either side of a movie or television screen with the bass unit placed in any convenient location. Since the bass unit location has not been generally considered critical, the bass unit has frequently been hidden behind or under any convenient piece of furniture. Such stereophonic systems have been very successful.
Four channel or quadraphonic sound systems comprising full-range right and left front stereo loudspeakers and full-range right and left rear loudspeakers were developed, however, the quadraphonic sound system was a marketing failure, particularly in the private home market. One of the reasons for the marketing failure is reputed to be the difficulty in placing four large separate loudspeakers in the proper locations about the listener for best acoustic reproduction which typically conflicts with other decorating and furniture placement considerations. Another reason often cited is the additional cost of the two full-range rear loudspeakers.
Recently, package systems have been introduced that comprise five physically small loudspeakers plus a larger subwoofer. The five small loudspeakers interfere less with room decor and the subwoofer location is flexible because of its frequency range. Long wires must be installed for the two rear loudspeakers and this factor has caused some customer resistance.
The Dolby® AC3™ system is now being marketed with five full-range loudspeakers or five small loudspeakers plus a subwoofer, however, customer acceptance has not yet been proven.
Applicant's previous U.S. Pat. No. 4,578,809 and U.S. Pat. No. 4,691,362 disclose dihedral loudspeakers with variable dispersion circuits. These circuits include delay lines that drive both high frequency drivers simultaneously within a loudspeaker plus circuit elements that differentiate the energy supplied to the drivers facing away from the expected listener location from the energy supplied to the drivers facing the listener location. This patent is incorporated by reference herewith.
Also, in the past, loudspeakers have been disclosed wherein a polar plot of the sound energy comprises a cardioid, the null in energy being on the axis of symmetry through the major lobe. Such a polar plot arises from loudspeakers as disclosed in Olson, Harry F., “Gradient Loudspeakers”, Journal of the Audio Engineering Society, Vol. 21, No. 2, March 1973, pp. 86–93.
Taking the polar plot a step further to a hypercardioid (which can be accomplished by varying the driving signal delay between the physically spaced speaker elements), the plot comprises a major lobe and a minor lobe, both lobes being symmetric about the same axis with symmetric nulls to each side of the axis. Where the major lobe and minor lobe are the same size (dipole) the nulls face directly opposite each other and are symmetric about a cross axis in turn perpendicular to the axis of symmetry of the lobes as shown by Olson (see also U.S. Pat. No. 4,961,226). Unequal lobes cause the nulls to face in equiangular directions relative to the axis of symmetry. Such polar plots arise from loudspeakers also disclosed by Olson. “Dipole” loudspeakers are described by Olson as gradient loudspeakers with zero electrical delay between the driver elements.
“Dipole” loudspeakers have been placed next to side walls with difference signals produced by electronic processing of the stereo signals supplied to the sidewall speakers. Such an arrangement can provide double dipole sidewall loudspeakers with nulls facing the audience and the walls in an auditorium setting. Such a configuration can be created by selecting one of the modes of operation of the sidewall loudspeakers as described in U.S. Pat. No. 5,301,237. In contrast, U.S. Pat. No. 4,819,269 discloses sidewall loudspeakers that broadcast over a 180° arc. The former of these disclosures teaches use of a five or seven channel surround sound processor whereas the latter teaches a two (stereo) channel sound source with additive or subtractive electric combinations of the two channels fed to the sidewall and rearwall loudspeakers.
The inventor of above U.S. Pat. No. 4,819,269 further develops his additive or subtractive approach to two channels fed to two loudspeakers in an article, Klayman, Arnold I., “Surround Sound With Only Two Speakers”, Audio, August 1992, pp. 32–37.
U.S. Pat. No. 4,847,904 and U.S. Pat. No. 5,117,459 disclose pairs of dihedral loudspeakers and additive or subtractive approaches to combining the electric signals from the right and left channels within the loudspeakers. In the former patent the outwardly directed drivers subtractively combine both channels and the inwardly directed drivers use a single channel. In the latter patent the channels are electrically combined in a different manner.
U.S. Pat. No. 4,888,804 discloses loudspeakers having the full range drivers directed to the listening area, limited range boundary drivers 180° out of phase directed a specific 65° from the full range drivers and in-phase limited range expansion drivers outwardly directed from the listening area. According to the patent, boundary drivers provide a cancellation of first arrival room boundary reflections as well as late arrival reflections. To restore the late arrival reflections which give a perception of spaciousness the in-phase expansion drivers restore the late arrival reflections.
Of interest is the research disclosed in Kantor, K. L. and DeKoster, A. P., “A Psycho-acoustically Optimized Loudspeaker”, Journal of the Audio Engineering Society, Vol. 34, No. 12, December 1986, pp. 990–996; wherein the optimal angles of the direct sound and the ambient sound maxima to the listener are 26° and 54°, 0° being defined as directly forward of the listener. Such an arrangement is said to cause minimum interaural cross-correlation.
Also of interest are recent articles on binaural recording and loudspeaker reproduction as well as transaural recording and reproduction in Griesinger, David, “Theory and Design of a Digital Audio Signal Processor for Home Use”, Journal of the Audio Engineering Society, Vol. 37, No. 1/2, January/February 1989, pp. 40–50; Griesinger, David, “Equalization and Spacial Equalization of Dummy-Head Recordings for Loudspeaker Reproduction”, Journal of the Audio Engineering Society, Vol. 37, No. 1/2, January/February 1989, pp. 20–29; and Cooper, Duane H., and Bauck, Jerold L., “Prospects for Transaural Recording”, Journal of the Audio Engineering Society, Vol. 37, No. 1/2, January/February 1989, pp. 3–19. The new loudspeaker surround sound technique disclosed below can be used to increase the robustness of the transaural techniques and significantly reduce the amount of signal processing required to achieve the desired acoustic effects.
Heretofore, stereo sound and surround sound have assumed multiple point sources for multiple channels with the point sources separated in space and optionally some cross-talk cancellation.